Cursor pointing devices have been used in connection with various types of computers and computer-related devices for a number of years. In the personal computer and workstation marketplaces, electronic mice have become widely accepted for their ease of use in graphics and other programs, and their advantages over most other cursor pointing devices are well known.
The trackball has also achieved a reasonable degree of acceptance among computer and workstation users, although not to the extent that the electronic mouse has become accepted. In part, this relative lack of acceptance relates to the design of prior art trackballs, which are frequently cumbersome to use. A typical prior art trackball, such as described in U.S. Pat. No. 4,562,347, consists of an enlarged polymeric ball which is centrally located within, and protruding from, a housing. A plurality of buttons, or switches, is typically located somewhere on the housing, most often at the top of the trackball. In use, the trackball is rotated within the housing by either the palm or the fingers, thereby causing the cursor on the video display to move. Once the cursor is moved to the desired location, one or more of the buttons are pressed (as appropriate for whatever software package is being run) to cause some desired action. In some applications, particularly graphics software, it is necessary to depress a button and, while holding the button down, rotate the ball to move the cursor from a beginning location to an ending location. This action, referred to as "click, drag and release", occurs in many modern software applications. Once the cursor reaches the ending location, the button is released and a desired function is performed.
This "click, drag and release" function cannot be readily performed by existing trackballs. Prior art trackballs, in recognition of this limitation, have in at least some instances offered a "click lock" function. In this operation, a click lock function is turned on, the ball is rotated to move the cursor, and the click lock function is released. In ergonomic terms, this requires the operator to first move the hand to a position where the click lock can be actuated, followed by moving the hand to the ball itself and performing the necessary rotation, finally followed by moving the hand back to a position where the click lock can be released. These relatively time consuming and complex hand movements have presented a limitation in the prior art. Prior art trackballs have typically required that the manipulation of the ball itself be done by removing the fingers from the buttons, so that operation of the trackball continually requires repositioning of the hand to perform nearly every task. This has been found to be cumbersome and undesirable, and has limited the acceptance of the trackball. There has therefore been a long felt need for a trackball in which the ball could be simultaneously manipulated while operating the buttons.